The present invention relates to a communication device for performing data communication by means of a DMT (discrete multi tone) data set method between communication devices. In particular, this invention relates to a communication device that performs interference rejection between TCM (Time Compression Multiplexing: time-shared transmission method)xe2x80x94ISDN and ADSL, or between ADSL and ADSL, relative to each other, and also relates to interference rejection method thereof.
A conventional communication device will first be described. At first, in a conventional communication device for performing data communication by means of a DMT (Discrete Multi Tone) data set method, the operation of a transmission system will be described briefly. For example, when data communication is to be performed with the DMT data set method, using an existing transmission line such as a telephone line or the like, in the transmission system, there is performed a tone ordering processing (thereby, the transmission rate is determined), that is, a processing for allocating transmission data having number of bits that can be transmitted, respectively, to a plurality of tones (multi carrier) of a frequency band set in advance based on a S/N ratio (signal-to-noise ratio). Specifically, for example, transmission data having number of bits corresponding to the respective S/N ratio are allocated to tones of from tone 0 to tone X (X is an integer showing the number of tones) in each frequency.
The transmission data are then multiplexed for each frame, by performing the tone ordering processing corresponding to the S/N ratio and a coding processing. Moreover, in the transmission system, inverse fast Fourier transform (IFFT) is performed with respect to the multiplexed transmission data, to convert parallel data after the inverse fast Fourier transform to serial data, and thereafter, the digital waveform is converted to the analog waveform through a D/A converter, which is finally subjected to a low-pass filter, and the transmission data is transmitted on the telephone line.
Operation of a reception system in a conventional communication device that performs data communication by means of a DMT data set method will now be described briefly. Similarly to the above case, when data communication is to be performed with the DMT data set method, using an existing transmission line such as a telephone line or the like, in the reception system, the received data (the above-described transmission data) is subjected to a low-pass filter, and thereafter, the analog waveform is converted to the digital waveform through an A/D converter, and an adaptive equalization processing of time domain is performed by a time domain equalizer.
The data subjected to the time domain adaptive equalization processing is converted from serial data to parallel data, which is then subjected to the fast Fourier transform. Thereafter, an adaptive equalization processing of frequency domain is performed by a frequency domain equalizer.
The data subjected to the frequency domain adaptive equalization processing is converted to serial data through a complex processing (complex method of maximum likelihood) and the tone ordering processing, and thereafter, processing such as rate convert processing, FEC (forward error correction), de-scramble processing, CRC (cyclic redundancy check) or the like is performed, to finally reproduce the transmission data.
As a wire system digital communication method that performs data communication using the above-described DMT data set method, there can be mentioned an XDSL communication method such as an ADSL (Asymmetric Digital Subscriber Line) communication method that performs high speed digital communication at several megabits per second, using an existing telephone line. This method is standardized in ANSI, T1.413 or the like. With this digital communication method, in particular, the ADSL transmission line and the ISDN transmission line in the ISDN communication system of a half duplex communication method are tied up at an aggregate line on the way and adjacent to each other. The ISDN communication system referred herein is a method heretofore adopted in NTT, for example, the TCM-ISDN service, which service is generally referred to as a ping-pong method.
FIG. 9 shows a signal flow in the TCM-ISDN service heretofore serviced by NTT. With this service, for example as shown in FIG. 9, ISDN-DS (Downstream) is transmitted from OCU (Office Channel Unit), that is, a base station, and the ISDN-DS is received by DSU (Digital Service Unit), that is, by a reception device side. Then, on the reception device side, after 7 UI (1 UI: 3.125 xcexcs) since having completed reception, ISDN-US (Upstream) is transmitted, and the ISDN-US is received by the base station side.
Specifically, with the above DSU, for example as shown in FIG. 9, a delay corresponding to the distance with OCU exists in the ISDN service. For example, if the distance between OCU and DSU is a short distance (here, a distance 0 is shown), there is no delay, and upon transmission of ISDN-DS by the OCU, the DSU receives the ISDN-DS. Moreover, ISDN-US transmitted from the DSU after 7 UI is transmitted to the OCU without any delay. On the other hand, if the distance between the OCU and the DSU is a long distance (here, a long distance limit is shown), when the OCU transmits ISDN-DS, the DSU receives the ISDN-DS after a predetermined delay time has passed. Moreover, ISDN-US transmitted from the DSU after 7 UI is transmitted to the OCU after a predetermined delay time has passed. Here, TTR (TCM-ISDN Timing Reference) shown in the figure is a signal serving as a reference for synchronization in the downstream and upstream on the network, and in the TCM-ISDN, this timing may be known only in the base station. Furthermore, one cycle of TTR is designated herein as, for example, 2.5 ms.
On the other hand, the ADSL transmission line is tied up with and adjacent to the above-described TCM-ISDN transmission line of the half duplex communication method at an aggregate line on the way. Hence, without timing adjustment between the ADSL and the TCM-ISDN, the TCM-ISDN signal becomes interference signal, thereby causing deterioration in the communication characteristic in the ADSL. That is to say, as shown in FIG. 10, NEXT (Near End Cross Talk) noise and FEXT (Far End Cross Talk) noise occur, causing deterioration in the communication characteristic in the ADSL.
Accordingly, in the ADSL service, as shown in FIG. 11 and FIG. 12, a boundary (dotted line shown in the figure) is provided, taking the delay into consideration, so as to be downstream at the time of DS of the TCM-ISDN, and to be upstream at the time of US of the TCM-ISDN. Here, FIG. 11 and FIG. 12 show a hyper-frame symbol form in the ADSL, respectively, and constitutes one hyper frame with, for example, 345 symbols. One hyper frame is designated herein as 85 ms, and this value is a multiple of TTR (2.5 ms) described above. Also, in FIG. 11 and FIG. 12, an example of a hyper frame including a cyclic prefix is shown, but similar operation is possible even in a hyper frame including no cyclic prefix. In this case, however, one hyper frame (345 symbols) becomes 80 ms.
Furthermore, a netted portion in FIG. 11 is referred to as FEXTR data symbol (indicating the time when the reception device side is in the FEXT period), and other data is referred to as NEXTR data symbol (indicating the time when the reception device side is in the NEXT period). Also, a netted portion in FIG. 12 is referred to as FEXTc data symbol (indicating the time when the base station side is in the FEXT period), and other data is referred to as NEXTc data symbol (indicating the time when the base station side is in the NEXT period).
Specifically, FEXT-DS transmission is performed by the ATU-C at the time of ISDN-DS transmission by means of the OCU, and FEXT-US transmission is performed by the ATU-R at the time of ISDN-US transmission by means of the DSU.
As a result, a conventional ADSL communication device is not affected by interference due to DS and US in the TCM-ISDN, and hence, communication characteristic is not deteriorated due to the TCM-ISDN.
However, with the above-described conventional communication device, influence of interference given by the ADSL to the TCM-ISDN and interference between ADSLs have not been considered.
At first, interference given by the ADSL to the TCM-ISDN will be specifically described. For example, as shown in FIG. 9, when the distance between the OCU and the DSU is xe2x80x9c0xe2x80x9d, since there is no delay, the transfer timing of ISDN-DS and the transfer timing of ISDN-US agree with each other, respectively, at a point of {circumflex over (1)} and at a point of {circumflex over (3)}. However, when the distance between the OCU and the DSU is a xe2x80x9clong distance limitxe2x80x9d,ISDN-DS is received delayed by 16 UI (50 xcexcs: between {circumflex over (1)} and {circumflex over (2)} in FIG. 1), and ISDN-US arrives similarly delayed by 16 UI (between {circumflex over (3)} and {circumflex over (4)} in FIG. 1). As a result, delay of 32 UI in total will occur. At this time, the ISDN-US reception in the OCU will exceed the boundary {circumflex over (5)} in the NEXT period.
Hence, the FEXTR data symbols (for example, symbol number 10, 81, 142, 213, 284) from the ATU-C enclosed by a circle shown in FIG. 11 become interference components (NEXT noise) with respect to the OCU in the TCM-ISDN, causing deterioration in the communication characteristic in the ISDN service. That is to say, there is such a problem in that reception by the OCU may be affected by interference due to the FEXT-DS transmission by the ATU-C.
Next, interference between ADSLs will be specifically described. For example, in the ADSL, the ATU-C is transmitting TTR to the ATU-R, as shown in FIG. 13. Therefore, the TTR held by the ATU-R will have a delay of maximum 20 UI (the delay becomes 20 UI, taking into consideration a margin with respect to the maximum delay time, 16 UI of the TCM-ISDN, but since the TCM-ISDN and the ADSL use substantially the same transmission line, the actual maximum delay time becomes 16 UI) depending on the distance of the transmission line. In this case, if it is assumed that the TTR of the ATU-R has a delay of 20 UI, the FEXT-US reception from the ATU-R that operates synchronously thereto will have a delay of not exceeding 40 UI.
At this time, in other ATU-Cs and its own ATU-C where hyper-frame synchronization is performed, for example, even in a case of symbol No. 81 shown in FIG. 11, since symbols up to symbol No. 79 are FEXT-US transmission, as seen from FIG. 12, interference will not occur even if the FEXT-US transmission is delayed by 40 UI at maximum. However, in other ATU-Cs where hyper-frame synchronization is not performed, the FEXT-DS transmission of the symbol No. 81 shown in the above FIG. 11 becomes interference in the FEXT-US reception just at the boundary, such as a symbol No. 39. That is to say, there is a problem in that the FEXT-DS transmission of the ATU-C becomes the NEXT noise with respect to the FEXT-US reception of other ATU-Cs.
Accordingly, in view of the above situation, it is an object of the present invention to provide a communication device that can perform interference rejection between the TCM-ISDN and ADSL, or between ADSLs relative to each other, and also provide an interference rejection method thereof.
With a communication device according to the present invention, it is characterized in that the communication device has a reference signal for synchronization with regard to the downstream and upstream, and performs data communication by means of the ADSL, by transmitting the reference signal to a device to be communicated to thereby establish mutual synchronization, the reference signal in its own communication device is delayed by a first predetermined time and a reference signal to be transmitted to the device to be communicated is approximately adjusted by a second predetermined time, to thereby reject all mutual interference occurring between other communication systems that communicate by utilizing a line having the same properties and using the same reference signal, and the ADSL, and all mutual interference occurring between ADSLs.
According to this invention, for example, the own communication device (ATU-C) shifts TTR (reference signal) in the own ATU-C by S1 (first predetermined time), so that FEXT-DS in the ATU-C is not involved in the ISDN-US reception of the ISDN (other communication system). Moreover, the ATU-C transmits its TTR to the ATU-R (a device to be communicated), with a variable delay S2 (second predetermined time) corresponding to the distance with the ATU-R added to the inside TTR delayed by S1 previously. That is to say, S2 is adjusted so that the FEXT-DS transmission of the ATU-C does not become interference in the FEXT-US reception of other ATU-C that is not synchronized therewith (hyper-frame synchronization). As a result, all the interference between the ADSL and the ISDN and between ADSLs relative to each other can be rejected.
With a communication device according to the next invention, it is characterized in that an allowable range of the first predetermined time is calculated based on a relational expression between a communication device on the transmission side and a communication device on the reception side where interference occurs most likely, and a value which maximizes the margin of the allowable range is fixed as the first predetermined time.
According to this invention, the first predetermined time is calculated using a relational expression at a point where interference occurs most likely under conditions of the maximum transmission line delay, that is, where the margin is smallest in the relational expression. As a result, a relational expression between devices having other conditions, for example, less possibility of interference can be easily compensated.
With a communication device according to the next invention, it is characterized in that an allowable range of the second predetermined time is calculated corresponding to the compensated range of the transmission line delay, based on a relational expression between all communication devices on the transmission side and all communication devices on the reception side, having a possibility that interference may occur, and the first predetermined time, and a value that always maximizes the margin is calculated, corresponding to a variation in the transmission line delay, and the calculated value is designated as the second predetermined time.
According to this invention, S1 (first predetermined time) and S2 (second predetermined time) can be uniquely calculated respectively from one corresponding relational expression, and in the ADSL, TTR (reference signal) is shifted by S1 and S2 calculated herein. As a result, all the interference between the ADSL and the ISDN and between ADSLs relative to each other can be rejected.
With a communication device according to the next invention, it is characterized in that an allowable range of the second predetermined time is calculated corresponding to the compensated range of the transmission line delay, based on a relational expression between all communication devices on the transmission side and all communication devices on the reception side, having a possibility that interference may occur, and the first predetermined time, so that even if the transmission line delay varies, the second predetermined time is fixed within the allowable range of the second predetermined time.
According to this invention, S2 (second predetermined time) is fixed in advance to a value satisfying the allowable range. As a result, the interference in the ISDN due to the ADSL and interference between ADSLs relative to each other can be rejected, and further, S2 can be fixed to a plurality of values. Hence, since it is not necessary to determine S2 by calculation of a relational expression, calculation amount decreases, thereby facilitating high speep processing. In addition, S2 can be fixed to one by designating S2 that is a relatively rare case in communication (a value close to the maximum value and the minimum value in the allowable range) as an optional function, thereby further decreasing the calculation amount and facilitating high speed processing.
With a communication device according to the next invention, it is characterized in that before establishing communication between devices in the ADSL, measurement of the transmission line delay between the devices and calculation of the first predetermined time and the second predetermined time are performed, thereby establishing communication without having any interference.
According to this invention, before the ATU-C and the ATU-R establish hyper-frame synchronization, the ATU-C calculates the transmission line delay. As a result, S1 (first predetermined time) and S2 (second predetermined time) for delaying the TTR (reference signal) can be easily calculated, hence enabling establishment of communication without having any interference.
With a communication device according to the next invention, it is characterized in that the transmission line delay is calculated based on round trip time of a certain signal between the devices.
According to this invention, since RTD (round trip time of a certain signal) is measured, the calculation becomes very easy, thereby reducing the processing time by the ATU-R. Moreover, for example, by communicating at the double frequency on the return trip, the frequency does not overlap in the first half and the second half, hence the ATU-C can easily recognize a signal from the ATU-R.
With interference rejection method according to the next invention, a reference signal in its own communication device is delayed by a first predetermined time and a reference signal to be transmitted to a device to be communicated is approximately adjusted by a second predetermined time, to thereby reject all mutual interference occurring between other communication systems that communicate by utilizing a line having the same properties, and using the same reference signal, and the ADSL, and all mutual interference occurring between ADSLS.
According to this invention, for example, the own communication device (ATU-C) shifts TTR (reference signal) in the own ATU-C by S1 (first predetermined time), so that FEXT-DS in the ATU-C is not involved in the ISDN-US reception of the ISDN (other communication system). Moreover, the ATU-C transmits its TTR to the ATU-R (a device to be communicated), with a variable delay S2 (second predetermined time) corresponding to the distance with the ATU-R added to the inside TTR delayed by S1 previously. That is to say, S2 is adjusted so that the FEXT-DS transmission of the ATU-C does not become interference in the FEXT-US reception of other ATU-C that is not synchronized therewith (hyper-frame synchronization). As a result, all the interference between the ADSL and the ISDN and between ADSLs relative to each other can be rejected.
With an interference rejection method according to the next invention, it is characterized in that an allowable range of the first predetermined time is calculated based on a relational expression between a communication device on the transmission side and a communication device on the reception side where interference occurs most likely, and a value which maximizes the margin of the allowable range is fixed as the first predetermined time.
According to this invention, the first predetermined time is calculated using a relational expression at a point where interference occurs most likely under conditions of the maximum transmission line delay, that is, where the margin is smallest in the relational expression. As a result, a relational expression between devices having other conditions, for example, less possibility of interference can be easily compensated.
With an interference rejection method according to the next invention, it is characterized in that an allowable range of the second predetermined time is calculated corresponding to the compensated range of the transmission line delay, based on a relational expression between all communication devices on the transmission side and all communication devices on the reception side, having a possibility that interference may occur, and the first predetermined time, and a value that always maximizes the margin is calculated, corresponding to a variation in the transmission line delay, and the calculated value is designated as the second predetermined time.
According to this invention, S1 (first predetermined time) and S2 (second predetermined time) can be uniquely calculated respectively from one corresponding relational expression, and in the ADSL, TTR (reference signal) is shifted by S1 and S2 calculated herein. As a result, all the interference between the ADSL and the ISDN and between ADSLs relative to each other can be rejected.
With an interference rejection method according to the next invention, it is characterized in that an allowable range of the second predetermined time is calculated corresponding to the compensated range of the transmission line delay, based on a relational expression between all communication devices on the transmission side and all communication devices on the reception side, having a possibility that interference may occur, and the first predetermined time, so that even if the transmission line delay varies, the second predetermined time is fixed within the allowable range of the second predetermined time.
According to this invention, S2 (second predetermined time) is fixed in advance to a value satisfying the allowable range. As a result, the interference in the ISDN due to the ADSL and interference between ADSLs relative to each other can be rejected, and further, S2 can be fixed to a plurality of values. Hence, since it is not necessary to determine S2 by calculation of a relational expression, calculation amount decreases, thereby facilitating high speed processing. In addition, S2 can be fixed to one by designating S2 that is a relatively rare case in communication (a value close to the maximum value and the minimum value in the allowable range) as an optional function, thereby further decreasing the calculation amount and facilitating high speed processing.
With an interference rejection method according to the next invention, it is characterized in that before establishing communication between devices in the ADSL, measurement of the transmission line delay between the devices and calculation of the first predetermined time and the second predetermined time are performed, thereby establishing communication without having any interference.
According to this invention, before the ATU-C and ATU-R establish hyper-frame synchronization, the ATU-C calculates the transmission line delay. As a result, S1 (first predetermined time) and S2 (second predetermined time) for delaying the TTR (reference signal) can be easily calculated, hence enabling establishment of communication without having any interference.
With an interference rejection method according to the next invention, it is characterized in that the transmission line delay is calculated based on round trip time of a certain signal between the devices.
According to this invention, since RTD (round trip time of a certain signal) is measured, the calculation becomes very easy, thereby reducing the processing time by the ATU-R. Moreover, for example, by communicating at the double frequency on the return trip, the frequency does not overlap in the first half and the second half, hence the ATU-C can easily recognize a signal from the ATU-R.
With an interference rejection method according to the next invention, it is characterized in that an allowable range of the first predetermined time is calculated based on a relational expression between a communication device on the transmission side and a communication device on the reception side where interference occurs most likely, and a value which maximizes the margin of the allowable range is fixed as the first predetermined time, the fixed first predetermined time being substituted in all the aforementioned relational expressions, and in this state, an allowable range of the second predetermined time is calculated based on a relational expression between a communication device on the transmission side and a communication device on the reception side where interference occurs most likely, and a value which maximizes the margin of the allowable range is fixed as the second predetermined time.
According to this invention, the first predetermined time and the second predetermined time are calculated without relying on conditions of the transmission line delay, using a relational expression where interference occurs most likely, that is, the margin is smallest in the relational expression. As a result, a relational expression between devices having other conditions, for example, less possibility of interference can be easily compensated. Moreover, since the first predetermined time and the second predetermined time are fixed values, it is not necessary to change the value every time depending on the conditions of the transmission line delay or the like, hence the calculation amount of each device can be reduced.
With an interference rejection method according to the next invention, it is characterized in that an allowable range of the first predetermined time is calculated based on a relational expression between a communication device on the transmission side and a communication device on the reception side where interference occurs most likely, and a value which maximizes the margin of the allowable range is fixed as the first predetermined time, the fixed first predetermined time being substituted in all the aforementioned relational expressions, and in this state, an allowable range of the second predetermined time is calculated based on a relational expression between a communication device on the transmission side and a communication device on the reception side where interference occurs most likely, and a value which maximizes the margin of the allowable range is fixed as the second predetermined time.
According to this invention, the first predetermined time and the second predetermined time are calculated without relying on conditions of transmission line delay, using a relational expression where interference occurs most likely, that is, the margin is smallest in the relational expression. As a result, a relational expression between devices having other conditions, for example, less possibility of interference can be easily compensated. Moreover, since the first predetermined time and the second predetermined time are fixed values, it is not necessary to change the value every time depending on the conditions of the transmission line delay or the like, hence the calculation amount of each device can be reduced.
With a communication device according to the next invention, it is characterized in that a delay resulting from the internal processing in communication devices on the transmission side and the reception side, and predetermined conditions for protecting the other communication systems from interference more strictly are newly added to the relational expression, and based on the relational expression reflecting these conditions, the first predetermined time and the second predetermined time are calculated.
According to this invention, the communication device calculates the first predetermined time and the second predetermined time, by adding new conditions to the relational expression, for example, a loop timing margin, a system margin, a guard interval in the ISDN, a condition for inhibiting transfers spanning the TTR cycle or the like. As a result, more precise first predetermined time and second predetermined time can be calculated, thereby enabling interference rejection between devices with higher precision.
With an interference rejection method according to the next invention, it is characterized in that a delay resulting from the internal processing in communication devices on the transmission side and the reception side, and predetermined conditions for protecting the other communication systems from interference more strictly are newly added to the relational expression, and based on the relational expression, reflecting these conditions, the first predetermined time and the second predetermined time are calculated.
According to this invention, the first predetermined time and the second predetermined time are calculated based on a relational expression obtained by adding new condition, for example, a loop timing margin, a system margin, a guard interval in the ISDN, a condition for inhibiting transfers spanning the TTR cycle or the like. As a result, more precise first predetermined time and second predetermined time can be calculated, thereby enabling interference rejection between devices with higher precision.